Duplicate of an object vanishes when starting the blender game
If you are duplicating the object with the animation then the animation is your problem.

See if you have the location keyframed the location is locked to those keyframes. If you duplicate and move that animated object, as soon as you play the animation both objects are going to be in the same place (same location in the animations).

This gif shows the problem


What you should do, and what X-27 said to do in the comments, is to add an empty in the same location as your coin. Then parent the coin to the empty. Now move the empty to position the coin. To duplicate it again, select both the coin and the empty and put them where you want.

In this gif I show how to duplicate animated objects.